1. Field of the Invention
The present invention is concerned with overfill and spillage protection devices employed in conjunction with underground fuel storage tanks typically utilized at gasoline service stations. Such tanks are filled from tank trucks through a fill pipe which extends upwardly from the tank to a coupling located within a relatively shallow manhole in the service station apron. During the filling operation, a supply hose from the tank truck is connected to the coupling.
It is quite common that the refilling operation overfills the tank, and when the supply hose is uncoupled from the fill pipe, excess fuel will spill from the fill pipe and uncoupled supply hose. Spillage can also occur from leaky supply hoses or couplings.
2. Description of Prior Art
Because it is obviously undesirable to allow the spillage of fuel to simply drain into the ground, particularly when the storage tank may be refilled on a weekly basis, some states presently require that overfill protection and storage devices be employed on all underground fuel storage tanks. An overfill and spillage protection device for this purpose is shown in U.S. Pat. No. 4,615,362.
In general terms, the overfill and spillage protection device of U.S. Pat. No. 4,615,362 takes the form of a generally cylindrical reservoir sealed at its lower end to the outer side of the storage tank fill pipe and extending upwardly beyond the upper end of the fill pipe in spaced surrounding relationship to the fill pipe so fuel which may spill from the top of the fill pipe or from a supply hose upon uncoupling of the hose from the fill pipe will be captured within the reservoir. Valve means are provided to drain fuel from the reservoir into the storage tank when the level of fuel within the fill pipe is lowered as fuel is withdrawn from the tank during usage.
The overfill reservoir of U.S. Pat. No. 4,615,362 is buried below ground level and is fixedly coupled to the upper end of the fill pipe, whose lower end in turn is fixedly coupled to the underground storage tank. The underground storage tank is massive and invariably buried at a depth well below the frost line. It is thus an immovable object which fixedly and rigidly anchors the fill pipe. The spillage reservoir, on the other hand, is located close to the ground surface with its upper end closed only by a metal cover directly exposed to the outside air temperature. In colder climates, particularly in variable weather conditions, the frost line may extend below the bottom of the overfill reservoir and the earth underlying the reservoir may alternately freeze and thaw over a period of several months. When the earth underlying the spillage reservoir freezes, it expands and can exert a substantial upward pressure against the bottom of the reservoir which places a substantial strain on the coupling and seal between the reservoir and fill pipe. This will ultimately result in leakage at the coupling which is extremely difficult to detect.
The present invention is especially directed to an improved form of overfill and spillage reservoir which is capable of absorbing forces applied to the reservoir by freezing and thawing.